Circuit board structure with embedded fine-pitch wires and fabrication method thereof

ABSTRACT

A formation method of circuit board structure is disclosed. The formation method comprises: forming an intermediate substrate having interconnections therein and circuit patterns on both upper and lower surfaces, wherein the interconnections electrically connect the upper and lower circuit patterns; forming an upper dielectric layer overlying the upper circuit patterns, wherein the upper dielectric layer has a plurality of trenches therein; forming conductive wires in the trenches using e-less plating; and forming at least one protective layer overlying the conductive wires using a surface finishing process. The circuit board structure features formation of embedded conductive wires in the dielectric layer so that a short circuit can be avoid.

FIELD OF THE INVENTION

This invention relates to a circuit board structure for BOL (bond on lead) process, and more particularly relates to a circuit board structure with embedded fine-pitch wires.

BACKGROUND OF THE INVENTION

A circuit board structure is widely applied in various electronic products, such as consumer electronic products. Because the consumer electronic products are getting more and more compact, the circuit board structure has to shrink its dimensions as well. This means that pitch, the sum of the line width d₁ and the spacing d₂ as shown in FIG. 2A, must be reduced so as to integrate more elements/devices on a more compact circuit board structure.

FIG. 1 illustrates a conventional circuit board structure. FIG. 2A and FIG. 2B are enlarged views of FIG. 1 illustrating formation of bump pads using a semi additive process. As shown in FIG. 1, the circuit board structure 1 includes an intermediate substrate 10 having interconnections 40 therein and circuit patterns (20, 30) on both upper and lower surfaces. The interconnections 40 electrically connect the upper and lower circuit patterns (20, 30). The circuit board structure 1 further includes an upper dielectric layer 50 overlying the upper circuit patterns 20. The upper dielectric layer 50 has a plurality of vias 70 for electrically connecting the upper circuit patterns 20 and an external circuit (not shown). The circuit board structure 1 further includes a lower dielectric layer 60 covering the lower circuit patterns 30. The lower dielectric layer 60 has a plurality of vias 80 for electrically connecting the lower circuit patterns 30 and the external circuit (not shown). The circuit board structure 1 further includes an upper solder mask layer 90 and bump pads 105 overlying the upper dielectric layer 50, and further includes a lower solder mask layer 100 covering the lower dielectric layer 60. The upper solder mask layer 90 and lower solder mask layer 100 respectively expose bump pads 105 and vias 80 for subsequent surface finishing process, e.g. electroless nickel electroless palladium immersion gold (ENEPIG) process. Referring to FIG. 2A, prior to the ENEPIG process, a so-called semi additive process (SAP) is used to form copper wires 13 with a spacing d₂, for example, of 30 μm between each other. Referring to FIG. 2B, after the ENEPIG process, bump pads 105 are made of nickel layer 14, palladium layer 15 and gold layer 16 conformally overlying the copper wires 13. The bump space d₃ between adjacent bump pads 105 is reduced and less than 20 μm so that a short circuit might occur.

Accordingly, a circuit board structure capable of solving the aforementioned drawbacks is desirable.

SUMMARY OF THE INVENTION

In view of the aforementioned drawbacks in prior art, one embodiment of the invention provides a circuit board structure. A formation method of circuit board structure is disclosed. The formation method comprises: forming an intermediate substrate having interconnections therein and circuit patterns on both upper and lower surfaces, wherein the interconnections electrically connect the upper and lower circuit patterns; forming an upper dielectric layer overlying the upper circuit patterns, wherein the upper dielectric layer has a plurality of trenches therein; forming conductive wires in the trenches using e-less plating; and forming at least one protective layer overlying the conductive wires using a surface finishing process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a conventional circuit board structure.

FIG. 2A is an enlarged view of FIG. 1 illustrating copper wires formed by a semi additive process.

FIG. 2B is an enlarged view of FIG. 1 illustrating bump pads formed by a surface finishing process.

FIG. 3 illustrates a circuit board structure in accordance with one embodiment of the present invention.

FIG. 4A and FIG. 4B are enlarged views of FIG. 3 illustrating formation of embedded fine-pitch wires.

FIG. 5A is an enlarged view of FIG. 3 illustrating formation of copper wires with a surface higher than that of the dielectric layer.

FIG. 5B illustrates that the surface of copper wires as shown in FIG. 5A is substantially coplanar with that of the dielectric layer after chemical mechanical polishing or grinding.

DETAILED DESCRIPTION OF THE INVENTION

The present invention may best be understood by reference to the following description in conjunction with the accompanying drawings, in which similar reference numbers represent similar elements. Any devices, components, materials, and steps described in the embodiments are only for illustration and not intended to limit the scope of the present invention.

FIG. 3 illustrates a circuit board structure in accordance with one embodiment of the present invention. FIG. 4A and FIG. 4B are enlarged views of FIG. 3 illustrating formation of embedded fine-pitch wires, i.e., copper wires 130 using e-less copper plating. The circuit board structure 5 of one embodiment for the invention features formation of embedded copper wires 130 in the dielectric layer prior to formation of bump pads 110 using the surface finishing process such as ENEPIG process, as described later. In other embodiments, the surface finishing process may be electroless nickel immersion gold (ENIG) process, electroless nickel electroless gold (ENEG) process, organic solder preservative (OSP) process, immersion silver process, immersion tin process, or hot air solder leveling (HASL) process.

As shown in FIG. 3, the circuit board structure 5 of this embodiment includes an intermediate substrate 10 having interconnections 40 therein and circuit patterns (20, 30) on both upper and lower surfaces. The interconnections 40 electrically connect the upper and lower circuit patterns (20, 30). The circuit board structure further includes an upper dielectric layer 50 overlying the upper circuit patterns 20. The upper dielectric layer 50 has a plurality of vias 70 for electrically connecting the upper circuit patterns 20 and an external circuit (not shown). The circuit board structure further includes a lower dielectric layer 60 covering the lower circuit patterns 30. The lower dielectric layer 60 has a plurality of vias 80 for electrically connecting the lower circuit patterns 30 and the external circuit (not shown). The circuit board structure 5 further includes an upper solder mask layer 90 and bump pads 105 overlying the upper dielectric layer 50, and further includes a lower solder mask layer 100 covering the lower dielectric layer 60. The upper solder mask layer 90 and lower solder mask layer 100 respectively expose bump pads 110 and vias 80 for subsequent surface finishing process, e.g. electroless nickel electroless palladium immersion gold (ENEPIG) process. In other embodiments, the surface finishing process may be electroless nickel immersion gold (ENIG) process, electroless nickel electroless gold (ENEG) process, organic solder preservative (OSP) process, immersion silver process, immersion tin process, or hot air solder leveling (HASL) process. The circuit board structure 5 of this embodiment differs from that shown in FIG. 1 in formation of embedded copper wires 130. That is, the copper wires 130 are embedded in the upper dielectric layer 50 instead of being formed on/over the upper dielectric layer. Referring to FIG. 3 again, the embedded copper wires 130 can be formed in the circuit board structure 5 using a so-called coreless process or other well-known processes.

As shown in FIG. 4A, prior to the ENEPIG process, the embedded copper wires 130 with a spacing d₆ of 30 μm between each other are deposited in the upper dielectric layer 50. The embedded copper wires 130 are formed in trenches having a depth d₅ of 20 μm. Noted that a spacing 125 with a depth d₄ ranging from 3 to 7 μm is left for subsequent formation of bump pads using the ENEPIG process. Noted that the pitch, i.e. the sum of the line width d₇ and the spacing d₆, may range between 2 μm and 40 μm in accordance with various embodiments.

Referring to FIG. 4B, after the ENEPIG process, the bump pads 110 are made of nickel layer 140, palladium layer 150 and gold layer 160 overlying the embedded copper wires 130. The bump space d₆ between adjacent bump pads 110 remains unchanged, i.e. 30 μm so that a short circuit can be avoid. In other embodiments, the bump space d₆ may be less or larger than 30 μm.

Referring to FIGS. 5A and 5B, the embedded copper wires 530 a can be alternatively formed by other processes. As shown in FIG. 5A, the copper wires 530 are formed with a surface higher than that of the dielectric layer 50. As shown in FIG. 5B, the copper wires 530 are subsequently subject to a planarization process such as a chemical mechanical polishing or grinding so that the surface of embedded copper wires 530 a is substantially coplanar with that of the dielectric layer 50. Thereafter, the aforementioned surface finishing process is performed on the embedded copper wires 530 a.

Although specific embodiments have been illustrated and described, it will be obvious to those skilled in the art that various modifications may be made without departing from what is intended to be limited solely by the appended claims. 

1. A formation method of circuit board structure, comprising: forming an intermediate substrate having interconnections therein and circuit patterns on both upper and lower surfaces, wherein the interconnections electrically connect the upper and lower circuit patterns; forming an upper dielectric layer overlying the upper circuit patterns, wherein the upper dielectric layer has a plurality of trenches therein; forming conductive wires in the trenches using e-less plating; and forming at least one protective layer overlying the conductive wires using a surface finishing process.
 2. The formation method of claim 1, wherein a surface of the conductive wires is lower than that of the upper dielectric layer so that a spacing in the trenches is left, and wherein formation of the at least one protective layer includes filling up the spacing using the surface finishing process.
 3. The formation method of claim 1, wherein a surface of the conductive wires is higher than that of the upper dielectric layer, and wherein a planarization process is performed on the surface of the conductive wires until it is substantially coplanar with that of the upper dielectric layer prior to formation of the at least one protective layer.
 4. The formation method of claim 1, wherein the surface finishing process is electroless nickel electroless palladium immersion gold (ENEPIG) process, electroless nickel immersion gold (ENIG) process, electroless nickel electroless gold (ENEG) process, organic solder preservative (OSP) process, immersion silver process, immersion tin process, or hot air solder leveling (HASL) process.
 5. The formation method of claim 4, wherein the at least one protective layer is a single layer or multiple layers.
 6. The formation method of claim 5 wherein the at least one protective layer is selected from a group consisting of nickel, palladium, gold, silver, tin, and combination thereof.
 7. The formation method of claim 1, wherein a coreless process forms the intermediate substrate.
 8. The formation method of claim 2, wherein the spacing has a depth ranging between 3 and 7 μm.
 9. A formation method of circuit board structure, comprising: forming an intermediate substrate having interconnections therein and circuit patterns on both upper and lower surfaces, wherein the interconnections electrically connect the upper and lower circuit patterns; forming an upper dielectric layer overlying the upper circuit patterns, wherein the upper dielectric layer has a plurality of trenches therein; forming copper wires in the trenches using e-less copper plating, wherein a surface of the conductive wires is lower than that of the upper dielectric layer so that a spacing in the trenches is left; and forming at least one protective layer overlying the conductive wires to fill the spacing up using a surface finishing process.
 10. A formation method of circuit board structure, comprising: forming an intermediate substrate having interconnections therein and circuit patterns on both upper and lower surfaces, wherein the interconnections electrically connect the upper and lower circuit patterns; forming an upper dielectric layer overlying the upper circuit patterns, wherein the upper dielectric layer has a plurality of trenches therein; forming copper wires in the trenches using e-less copper plating, wherein a surface of the conductive wires is higher than that of the upper dielectric layer; performing a planarization process on the surface of the conductive wires until it is substantially coplanar with that of the upper dielectric layer; and forming at least one protective layer that covers the conductive wires only. 